(1) Field of the Invention
The present invention relates to a method and apparatus for improving the image quality of a display apparatus which may have a low response speed, such as a liquid crystal display apparatus.
(2) Description of the Related Art
For displaying a moving image on a liquid crystal display apparatus, the response time of a liquid crystal panel is preferably limited to one frame period (16 ms) or shorter. Some systems utilize an overdrive or an OCB (Optically Compensated Bend) liquid crystal technique in order to accomplish such a reduced response time.
The response time of the liquid crystal panel is generally represented by the sum of the time required to change the display state from a fully black image to a fully white image, and the time required to change the display state from a fully white image to a fully black image. The employment of the overdrive and OCB liquid crystal techniques has resulted in the provision of liquid crystal panels which have a response that is less than 16 ms.
However, even if the response time of the liquid crystal panel can be reduced to 16 ms or less, a retinal after-image phenomenon causes a blurred moving image. A blur of a moving image caused by a retinal after-image refers to a phenomenon in which, when a rapidly moving image is displayed, the moving image appears to be a blurred moving image because a retinal after-image of an image of a current frame is overlaid on an image of the next frame. This blur in a moving image due to retinal after-images is particularly conspicuous in a hold-type drive display apparatus which holds an image through one frame period.
Therefore, a panel driving apparatus has been provided for controlling the blur in a moving image due to the retinal after-image. This is a pseudo-impulse liquid crystal panel driving system in which a period of time, in which a panel is not illuminated with lights, is set in a period during which one frame is displayed. Details of the pseudo-impulse liquid crystal driving system are described in JP-A-2003-270669 (hereinafter called “Patent Document 1), and “Special Feature: Flat Panel Wars—Second Part,” Nikkei Electronics, No. 2002/11/18, pp. 110-118 (hereinafter called “Non-Patent Document 1”). According to this pseudo-impulse liquid crystal panel driving system, a fully black image is inserted into a frame period to reduce a retinal after-image and to restrain the blur in a moving image.
However, in the pseudo-impulse liquid crystal panel driving system as described in Patent Document 1 and Non-Patent Document 1, since the panel does not emit light during the black display duration, a problem arises that the luminance is correspondingly reduced. While Non-Patent Document 1 describes a solution for the problem of reduced luminance by increasing the numerical aperture of the panel, such a solution, involving a modification to the structure of the panel, will be expensive.